avoid passing unnecessary options to download method

The option --unicode-beta for tool/downloader.rb introduced in
r66448 must not be passed as an option to actual download machinery.
Thanks to MSP-Greg (Greg L.) for bug report and patch.
This closes issue #15434.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66449 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

tool/downloader.rb

@@ -124,6 +124,11 @@ class Downloader
     options = options.dup
     url = URI(url)
     dryrun = options.delete(:dryrun)
+
+    # remove from options (future use, see r66448), see L166
+    unicode_beta = options.delete(:unicode_beta)
+    puts "never" if unicode_beta == 'assigned but unused variable...'
+
     if name
       file = Pathname.new(under(dir, name))
     else